Meter Box SWA Meter Tails

Pentrep

Hi I'm installing 3 x 25 Sq SWA meter tails from meter box to CU (distribution board) for a new build standard 12 kVA domestic supply, larger cable size required due ET101:2008 A2 installation type derating 16 Sq T&E to below 63A. I have a 20M run so will also be fitting a 63A main overcurrent device in meter cabinet. My question is what is the acceptable way of glanding the SWA in the meter cabinet?

Is the following sufficient:
Gland SWA into Meter Box by drilling dedicated hole in enclosure. Terminate 2.5 Sq earth cable from gland armour using piranha earth nut with main 25 Sq earth protective conductor in the neutralising link. Since only the phase conductor is permitted in the MOD, glanding the SWA into the MOD enclosure would not be permitted.

Bruthal

I have a tendency to gland into steel boxes, like 4x4 ones in similar situations, if I was doing this type of job. Inner cable then out through a gland on the other side of the 4x4 box.

If it was me id prefer to earth the SWA back to the MET in DB.

2011

The SWA cable armour only needs to be tied to earth at one end, so as Burthal says this could be dealt with at the distribution board.

In the meter cabinet you could cut the armour off neatly and then put black heat shrink over it to finish (so as to ensure no sharp ends). You could then use a stuffing gland on the inner insulation of the SWA to gland it to the enclosure for the 63A main overcurrent device in meter cabinet.

JL spark

Do you not have to have a suitable gland on each end , I was pulled on this by my inspector

2011

JL spark wrote: »

Do you not have to have a suitable gland on each end , I was pulled on this by my inspector

In this case I am suggesting an SWA gland on one end ensuring that the armor is connected to earth on the other end there will be a stuffing gland (360 degree connection). As the armor is not the CPC (the is provided by a core within the cable) this is compliant unless there is something in the rules that says different.





(I can imagine someone desperately checking right now)

Pentrep

Thanks all for quick responses. Would ESB have any issue with metal box inside the meter box considering the meter box has to be made of a non conductive material?

2011

Pentrep wrote: »

Thanks all for quick responses. Would ESB have any issue with metal box inside the meter box considering the meter box has to be made of a non conductive material?

I can’t see a problem with that but its up to the ESB.
You could gland it into a 25 mm conduit box as this cable size takes a 25mm gland:

https://www.enfieldelectrical.co.uk/pages/swa-cable-gland-chart

Pentrep

2011 wrote: »

The SWA cable armour only needs to be tied to earth at one end, so as Burthal says this could be dealt with at the distribution board.

In the meter cabinet you could cut the armour off neatly and then put black heat shrink over it to finish (so as to ensure no sharp ends). You could then use a stuffing gland on the inner insulation of the SWA to gland it to the enclosure for the 63A main overcurrent device in meter cabinet.

What would prevent the armour from damaging the XLPE insulation of each condutor or the filling material if an SWA gland isn't used. Is the heat shrink placed over the armour?

Bruthal

Pentrep wrote: »

What would prevent the armour from damaging the XLPE insulation of each condutor or the filling material if an SWA gland isn't used. Is the heat shrink placed over the armour?

The armour when cut neatly will not damage the sheath that is over the insulated conductors.

2011

Pentrep wrote: »

What would prevent the armour from damaging the XLPE insulation of each condutor or the filling material if an SWA gland isn't used. Is the heat shrink placed over the armour?

My suggestion was to strip off the outer PVC and armor at the same point with a hacksaw (as normal). Then place a piece of heat shrink that extends about 40mm either side of where the armor was stripped and shrink it on. That way the full cable goes into the heat shrink and the inner insulation (often grey) containing the 3 insulated cores comes neatly out the other side. The armor won’t damage the insulation. The conductor is protected by 2 layers of insulation.

Bruthal

2011 wrote: »

You could gland it into a 25 mm conduit box as this cable size takes a 25mm gland:

Yea that can be done with a straight through box.

Podge201

I always earth the strands at both ends. Just my preference.

2011

Podge201 wrote: »

I always earth the strands at both ends. Just my preference.

So would I when practical. I am just trying to offer an alternative.

2011

Bruthal wrote: »

Yea that can be done with a straight through box.

Yes, that is what I mean. SWA gland one side, bushing the other.

Podge201

2011 wrote: »

So would I when practical. I am just trying to offer an alternative.

I have never had a situation where it was impractical to earth both ends.

2011

Podge201 wrote: »

I have never had a situation where it was impractical to earth both ends.

Suppose you had an SWA glanding into something plastic ? Yes you could put an SWA gland on it but if you tighten is as much as you should for a proper earth connection with the armor. The risk is you may strip the plastic threads or damage the plastic enclosure. So it defeats the purpose of the gland. Also in many cases the earth tag / banjo will not fit inside the enclosure (such as a commando socket) so it must be external which frequently won’t work.

Tuco88

I agree, You will find alot of stuff in industrial and commercial work is made out of platic or fibreglass. One end of the S.W.A earthed is pretty common and acceptable.

In some case's you will see an external bango with a fly lead connected to a conduit or exposed conductive part.

Jayzee.

Prob doesn't matter here but afaik good practice is to gland at the supply side

I think I'm right in saying you could have problems with disconnection times on final circuits if the swa was glanded only at the far end

If the swa was then cut accidentally near the supply end

JL spark

Pentrep wrote: »

Thanks all for quick responses. Would ESB have any issue with metal box inside the meter box considering the meter box has to be made of a non conductive material?

You won’t have room , esb meter ,esb isolater , tails protection and now your steel box 4x4 or 4x6

JL spark

Jayzee. wrote: »

Prob doesn't matter here but afaik good practice is to gland at the supply side

I think I'm right in saying you could have problems with disconnection times on final circuits if the swa was glanded only at the far end

If the swa was then cut accidentally near the supply end

If you only earth the swa at the meter side , don’t forget to run a cpc to earth the amour at the meter box

Jayzee.

JL spark wrote: »

If you only earth the swa at the meter side , don’t forget to run a cpc to earth the amour at the meter box

What other way is there of doing it, obviously you have to connect the swa at one end

JL spark

Jayzee. wrote: »

What other way is there of doing it, obviously you have to connect the swa at one end

I’ve seen some earthed from the neutralising link , that was my point , has to be from DB

2011

Jayzee. wrote: »

I think I'm right in saying you could have problems with disconnection times on final circuits if the swa was glanded only at the far end

As always the disconnection time will be a function of:
1) The earth fault loop impedance.
2) The rating and characteristics of the protective device.

When a disconnection time is calculated for a circuit within a steel conduit the CPC within the conduit used, not the conduit itself.

Jayzee.

JL spark wrote: »

I’ve seen some earthed from the neutralising link , that was my point , has to be from DB

Don't agree with that

If you have a metallic enclosure at the supply side you would need to earth the swa and enclosure from the supply side imo

JL spark

Jayzee. wrote: »

Don't agree with that

If you have a metallic enclosure at the supply side you would need to earth the swa and enclosure from the supply side imo

I’m not saying I’m right or you , this is what safe electric told me ,

Bruthal

JL spark wrote: »

I’m not saying I’m right or you , this is what safe electric told me ,

They are not infallible. There should only be 1 neutralising conductor, and the swa should not be part of it imo. Anything earthed should be connected to the DB MET.

Bruthal

JL spark wrote: »

If you only earth the swa at the meter side , don’t forget to run a cpc to earth the amour at the meter box

Jayzee. wrote: »

What other way is there of doing it, obviously you have to connect the swa at one end

Well if earthing at one end, running a long earth wire from the DB to the meter end would seem less intuitive than simply earthing the end at the DB.

Pentrep

JL spark wrote: »

You won’t have room , esb meter ,esb isolater , tails protection and now your steel box 4x4 or 4x6

Agree the meter box is already fairly conjested.

Pentrep

Bruthal wrote: »

Well if earthing at one end, running a long earth wire from the DB to the meter end would seem less intuitive than simply earthing the end at the DB.

Agree would be somewhat impracticle to run an additional earth cable in parallel with the SWA from the meterbox back to the DB MET. I am leaning towards the suggestion of heat shrinking the armour in the meterbox (no metal box due to space restrictions) and just earthing at the DB end. Maybe it could be argued with Safe Electric that it is not reasonably possible to gland both ends. Extract from the Safe Electric December 2018 newsletter below.

Adequate electrical conductance shall be provided between metal sheaths or armouring of cables and the earthing terminals of equipment. This requires proper design. A proprietary gland is usually required. Please gland both ends of SWA cables (where possible).

2011

Pentrep wrote: »

Maybe it could be argued with Safe Electric that it is not reasonably possible to gland both ends.

A better argument with Safe Electric is that you are in compliance with the rules. They can not force you to do anything that is not in the rules.

Adequate electrical conductance shall be provided between metal sheaths or armouring of cables and the earthing terminals of equipment. This requires proper design. A proprietary gland is usually required. Please gland both ends of SWA cables (where possible).

......and glanding at the DB end with an SWA gland and earthing the armour there does exactly this.

Lwaker.

"Adequate conductance"

Is that in et101?

Pentrep

Lwaker. wrote: »

"Adequate conductance"

Is that in et101?

Yes I believe so. Taken from Safe Electric December 2016 newsletter, references Rule 526.5.2

I'm working from home at the moment so can't check ET101.